What drives the positive correlation between human population density and bird species richness in Australia?

Abstract

Aim To test six hypotheses that could explain or mediate the positive correlation between human population density (HPD) and bird species richness while controlling for biased sampling effort. These hypotheses were labelled as follows: productivity (net primary productivity, NPP); inherent heterogeneity (diversity of vegetation types); anthropogenic heterogeneity (diversity of land uses); conservation policy (proportion of conservation land); increased productivity (humaninduced productivity increases); and the reduced-slope hypothesis (which predicts that humans have a negative impact on species numbers across the full range of variation in HPD). Location Australia.Methods All data were collected at a spatial resolution of 1°across mainland Australia. Bird species richness was from 2007 atlas data and random subsampling was used to account for biased sampling effort. HPD was from the 2006 census. All other data were from government produced geographic information system layers. The most important biotic or abiotic factors influencing patterns in both species richness and HPD were assessed using simultaneous autoregressive models and an information theoretic approach.Results NPP appeared to be one of the main factors driving spatial congruence between bird species richness and HPD. Inherent habitat heterogeneity was weakly related to richness and HPD, although an interaction between heterogeneity and NPP indicated that the former may be an important determinant of species richness in low-productivity regions. There was little evidence that anthropogenic landscape heterogeneity or human-induced changes in productivity influenced the relationship between species richness and HPD, but conservation policy appeared to act as an important mediating factor and species richness was positively related to the proportion of conservation land only in regions of high HPD. Main conclusionsThe spatial congruence between bird species richness and HPD occurs because both respond positively to productivity and, in certain circumstances, habitat heterogeneity. Our results suggest that conservation policy could mediate this relationship, but further research is required to determine the importance of conservation reserves in supporting species in regions densely populated by humans.

Human impact and species richness of terrestrial vertebrate: a review at different macroecological scales

“…Sin embargo, a extensiones más regionales también emergen correlaciones de signo negativo (véase el estudio de Koh et al 2006 en el norte de Taiwán). Finalmente, para la región de Australia, únicamente se han realizado dos estudios hasta el momento, a un tamaño de grano de 1º x 1º y a nivel de ecorregiones (Luck et al 2004(Luck et al , 2010. Aunque todos los taxones de tetrápodos están representados en estas dos publicaciones, la escasez de trabajos para esta región sugiere una clara necesidad de realización de estudios futuros, sobre todo a escalas regionales.…”

“…Con este fin, ha existido un gran interés en documentar la coincidencia espacial entre DPH y riqueza de especies para diferentes grupos taxonómicos y regiones biogeográficas. Por ejemplo, numerosas publicaciones han mostrado que DPH se correlaciona positivamente con la riqueza de especies para vertebrados terrestres africanos (Balmford et al 2001), en Europa (Araújo 2003), Australia y Norte América (Luck et al 2004(Luck et al , 2010 o para toda una clase taxonómica (Mammalia) a extensión global y regiones biogeográficas (Torres-Romero y Olalla-Tárraga, datos sin publicar). Sin embargo, Pautasso (2007) y Beck et al (2012 sugieren que podría existir un efecto de la escala espacial de análisis (extensión geográfica y tamaño de grano), de tal manera que cabría esperar que la relación negativa entre impacto humano y riqueza de especies fuese más fácilmente detectable a extensiones regionales, y contrariamente una correlación positiva a extensiones más amplias (por ejemplo, continentales y/o globales).…”

The use of Australian bioregions as spatial units of analysis to explore relationships between climate and songbird diversity

“…Another problem with grid cells, but not bioregions, is that they have unequal land area when they span large latitudinal gradients or coastal lines. Luck et al (2010) reported a low correlation between cell size and richness implying that area is not a key factor in driving richness suggesting this sample bias inherent in grids was not an important issue. This conclusion is at odds with our species accumulation analyses, and may reflect that Luck et al (2010) did not control for bioregion.…”

“…Luck et al (2010) reported a low correlation between cell size and richness implying that area is not a key factor in driving richness suggesting this sample bias inherent in grids was not an important issue. This conclusion is at odds with our species accumulation analyses, and may reflect that Luck et al (2010) did not control for bioregion. For example, coastal grid cells with small proportion of land cover will have higher richness that grid cells from the arid zone with 100% land cover because of differences in primary productivity.…”

“…Luck et al (2010) attempted to remove sampling bias from the Australian bird distributional data by using a random sample of observations from each grid cells in the lattice, an approach which necessarily reduces estimates of species richness. Another problem with grid cells, but not bioregions, is that they have unequal land area when they span large latitudinal gradients or coastal lines.…”